Method of reconstituting nylon by solution in formic acid and distillation with hydrocarbon



Oct. 31, 1961 J. SIMON 3,006,867

' METHOD OF RECONSTITUTING NYLON BY SOLUTION IN FORMIC ACID AND DISTILLATION WITH HYDROCARBON Filed Jan. 31, 1958 Q 2N 3 0 g v m u... \r O N g INVENTOR cK S/MQ/V BY LEM A ORNEY oui ,a

United States Patent Ofiice 3,006,867 Patented Oct. 31, 1961 3,666,861 METHOD OF RECONSTITUTING NYLON BY SO- LUTION IN FGRMIC ACID AND DISTILLATION WITH HYDROCARBON Jack Simon, Paterson, N.J., assignor to General Plastics Filed Jan. 31, 1958, Ser. No. 712,437 4 Claims. (Cl. 2602.3)

My invention relates to a process of reconstituing nylon and more particularly to reconstituting nylon from textile wastes of nylon fibers.

Nylon is the name applied to a group of synthetic plastics which are long-chain polymeric amides in which the amide groups form an integral part of the main polymer chain, which have the characteristic that when formed into a filament, the structural elements are oriented in the direction of the axis. It is to be understood that when I use the term nylon throughout the specification and in the claims it shall mean such longchain polymer amides. Nylon has many uses and when originally produced by the reaction of adipic acid and hexamethylene diamene forms fine filament fibers of silklike appearance and having great strength, elasticity, and toughness. Such fibers are spun into yarns which are widely used for weaving and knitting fabrics.

Formic acid is a solvent for nylon. It has been attempted to recover nylon from textile wastes by dissolving such wastes in formic acid. Such nylon as has been recovered is degraded and discolored. Formic acid is expensive so that any method of attempting to recover nylon by its use must include steps for recovering the formic acid solvent. Distillation of formic acid from a solution of formic acid and nylon at atmospheric pressure always leads to discoloration of the nylon owing to the comparatively high temperatures involved. While formic acid boils at 100.7 C. at normal atmospheric pressure of 760 mm. of mercury, nylon absorbs formic acid so tenaciously that much higher temperatures than the boiling point are required to drive it ofi. Recovery of formic acid under subatmospheric pressure proceeds satisfactorily until the solution being distilled contains a residual of about 50 percent of formic acid. At this point the solution turns solid. It has always been found that large losses of formic acid occur when vacuum distillation is attempted. Owing to these difiiculties, therefore, there has been no attempt commercially to reconstitute nylon from textile wastes.

I have discovered that I can reconstitute nylon from textile wastes without degradation and discoloration and with reduced losses of formic acid by the use of a binary azeotropic mixture of formic acid and certain hydrocarbons. After a solution of nylon is formed in formic acid I admix a suflicient quantity of a predetermined hydrocarbon to form with the formic acid an azeotropic mixture. In this manner I am enabled to reduce the distillation temperature at which the azeotropic mixture may be recovered to such point that there is no degradation or discoloration of the nylon.

One object of my invention is to provide a method for the recovery of nylon from textile wastes in such a manner as to prevent degradation and discoloration of the nylon.

Another object of my invention is to provide a method of recovering nylon from textile wastes by the use of formic acid at reduced temperature and without the aid of subatmospheric pressure.

Another object of my invention is to provide a method of reconstituting nylon from textile wastes and the like by means of an azeotropic mixture whereby to avoid large losses of formic acid during the formic acid recovery step.

Other and further objects of my invention will appear from the following description.

The accompanying drawing which forms part of the instant specification and is to be read in conjunction therewith is a schematic view of one form of apparatus capable of carrying out the process of my invention.

In general my invention contemplates dissolving textile wastes in formic acid. After the solution has been formed, it is filtered to remove foreign material, titanium dioxide and other extraneous materials. The filtered solution is passed into a distillation zone and mixed with a hydrocarbon selected from the class of normal hexane, normal heptane, cyclohexanc, hexene, cyclohexene, benzone, and toluene to form an azeotropic mixture of the hydrocarbon and formic acid solvent. It is to be understood that while I prefer a binary mixture of formic acid and one of these hydrocarbons, a ternary mixture of formic acid and two of the hydrocarbons may be employed. Each azeotropic mixture behaves on distillation as a single chemical individual. The distillate will have the same composition as the original azeotropic mixture. The following table will give the compositions and azeotropic temperatures of suitable mixtures. The boiling point is given for the normal 760 mm. pressure. It is to be understood, of course, that if the pressure is altered, the boiling point and the composition of the mixture also vary.

Azeotropic Percent of Percent of After the correct azeotropic mixture of formic acid and the solvent is formed in the distillation zone, the azeotropic mixture is distilled to remove the solvent. If no agitation occurs during the distillation, the nylon is recovered as a light-colored mass. If intensive agitation takes place during the distillation step the nylon will be recovered in the form of small particles.

More particularly, referring now to the drawing, formic acid from any suitable source passes through pipe 10 and is pumped by pump 12 into the mixing chamber 14 into which scrap nylon is introduced through hopper 16. The nylon scrap may take any'form but advantageously may be textile wastes which have been cut up into small pieces for ease in handling. An agitator propeller 18 driven by motor 20 aids in the rapid solution of the nylon in the formic acid. Commercial formic acid which has a purity in the order of formic acid content may be employed. Sufiicient nylon scrap is added to bring the concentration of nylon in the solution to between 10 and 20 percent. It is to be understood, of course, that a smaller percentage of nylon may be employed if desired and a greater percentage may be added if desired. The solution becomes extremely viscous at about 40 percent nylon and tends to become gelatinous. If the mixture is too viscous, the filtering step is interfered with and pumping becomes diificult. I have found that a solution of about 15 percent nylon can be conveniently handled and processed. The solution of nylon is formic acid formed in the mixing chamber 14 is then pumped by pump 22 through a filter press 24 to remove dirt, titanium dioxide and other extraneous materials; The filtered solution of nylon in formic acid leaves the filter 24 through pipe 26 and passes into the still 28. When a predetermined quantity of solution is in the still as determined by the sight glass 30 the pump 22 is stopped and hydrocarbon from any suitable source is pumped through pipe 32 by pump 34 through pipe 36 into the still 28. During this pumping operation valve 38 will be open and valve 40 will be closed. A sufiicient quantity of the hydrocarbon selected from the class consisting of normal hexane, normal heptane, cyclohexane, hexene, cyclohexene, benzene, and toluene is pumped into the still 28 to form the desired azeotropic mixture with the formic acid solvent. The presence of the nylon in the formic acid solution does not interfere with the formation of the azeotropic mixture. The quantity of the particular hydrocarbon pumped into the still is set forth in the above table. It is to be understood, of course, that mixtures of hydrocarbon could be employed without departing from the spirit of my invention. The azeotropic temperatures of mixtures will vary from those of pure hydrocarbon as will be readily understood by those skilled in the art.

During the formation of the azeotropic mixture the impeller 42 positioned in the still is driven by motor 44 to thoroughly incorporate the hydrocarbon with the formic acid nylon solution. After the azeotropic mixture is formed the pump 34 is stopped and steam is introduced through pipe 46 under the control of valve 48 through the heat exchanger coil 50 positioned in the bottom of the still 28. The valve 48 may be controlled to maintain the desired azeotropic temperature within the still to boil off the azeotropic mixture of formic acid and the hydrocarbon. The hylotropic properties of the azeotropic mixture enable the mixture to change from the liquid phase to the vapor phase without change in its composition as if it were a single compound. The combined hydrocarbon and formic acid vapors leave the still 28 through pipe 52 and pass through a condenser 54 to which cooling water is supplied through pipe 56 under the control of valve 58. The condensate passes through pipe 60 into a separator 62. Here upon settling the formic acid will drop to the bottom and form a layer 64 and the hydrocarbon will form an upper layer 66. This hydro carbon may be reused and delivered by pump 34 to the next base to be treated by closing valve 38 and opening valve 40. Hydrocarbon may be Withdrawn from the separator through pipe 68 under the control of valve 70. The formic acid is withdrawn through pipe 72 under the control of valve 74 and may be reused in the process.

During the distillation step the impeller 42 is operated continuously in order that the nylon may be recovered as small particles. These particles 88 will collect at the bottom of the still.

After the distillation has been completed and all of the azeotropic mixture has been driven from the nylon, the steam is shut off and the still allowed to cool. At this time a manhole cover 82 is removed and the nylon particles taken from the bottom of the still.

The particles will be whitish in appearance and colorless and have irregular shapes and texture. The particles may be used in the same manner as the original nylon from which the Wastes were manufactured.

It will be seen that I have accomplished the object of my invention. I have provided a method of recovering nylon from textile wastes in such a manner as to prevent degradation and discoloration of the nylon. I have provided a method of recovering formic acid from the nylon solution by distillation at a reduced temperature without the aid of subatmosphen'c pressure. My method is such that large losses of formic acid during the formic acid recovery step are avoided.

It will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations. This is contemplated by and is within the scope of my claims. It is further obvious that various changes may be made in details within the scope of my claims without departing from the spirit of my invention. It is therefore to be understood that my invention is not to be limited to the specific details shown and described.

Having thus described my invention, what I claim is:

l A method of reconstituting a synthetic plastic comprising a long-chain polymeric amide in which the amide groups form an integral part of the main polymer chain which includes the steps of dissolving waste material formed of said synthetic plastic in formic acid, mixing a hydrocarbon selected from the group consisting of n-hexane, n-heptane, cyclohexane, hexene, cyclohexene, benzene, and toluene with the solution in an amount sufficient to form an azeotropic mixture, then heating the azeotropic mixture to a temperature sufiiciently high to vaporize the azeotropic mixture and removing the vapors from the distillation zone to leave behind the desired said synthetic plastic.

2. A method of reconstituting a synthetic plastic comprising a long-chain polymeric amide in which the amide groups form an integral part of the main polymer chain which includes the steps of dissolving waste material formed of said synthetic plastic in formic acid, mixing a hydrocarbon selected from the group consisting of nhexane, n-heptane, cyclohexane, hexene, cyclohexene, benzene, and toluene with the solution in an. amount suflicient to form an azeotropic mixture, then heating the azeotropic mixture to a temperature sufficiently high to vaporize the azeotropic mixture, removing the vapors from the distillation zone to leave behind the desired said synthetic plastic, condensing the vapors, separating the condensate to form a layer of a hydrocarbon and a layer of formic acid and introducing the hydrocarbon into the azeotropic mixture forming step as the hydrocarbon in the azeotropic mixture of a succeeding cycle.

3. A method of recovering a synthetic plastic comprising a long-chain polymeric amide in which the amide groups form an integral part of the main polymer chain from scrap material bearing said synthetic plastic including the steps of dissolving the said synthetic plastic scrap in formic acid to form a solution of said synthetic plastic in formic acid, filtering the solution to remove extraneous material, introducing a hydrocarbon selected from the class consisting of n-hexane, n-heptane, cyclohexane, hexene, cyclohexene, benzene, and toluene into the solution in such quantity as to form an azeotropic mixture, heating the resulting mixture in a distillation Zone to a temperature sufliciently high to vaporize the azeotropic mixture, removing the vapors from the distillation zone to leave behind the desired said synthetic plastic and then removing the said synthetic plastic from the distillation zone.

4. A method of reconstituting a synthetic plastic comprising a long-chain polymeric amide in which the amide groups form an integral part of the main polymer chain from Waste material containing said synthetic plastic including the steps of dissolving the said synthetic plastic of the waste material in formic acid, mixing a hydrocarbon selected from the class consisting of n-hexane, n-heptane, cyclohexane, hexene, cyclohexene, benzene, and toluene with the solution in a quantity sufiicient to form an azeotropic mixture, heating the resulting mixture in a distillation zone to a temperature sufiiciently high to vaporize the azeotropic mixture of formic acid and the hydrocarbon whereby to leave behind the desired said synthetic plastic and agitating the mixture during the distillation step to reduce the said synthetic plastic being recovered to particles.

References Cited in the file of this patent UNITED STATES PATENTS 2,447,732 Campbell et a1. Aug. 24, 1948 2,540,885 Hurst et al Feb. 6, 1951 2,623,862 Boyd Dec. 30, 1952 FOREIGN PATENTS 670,693 Great Britain April 1952 

1. A METHOD OF RECONSTITUTING A SYNTHETIC PLASTIC COMPRISING A LONG-CHAIN POLYMERIC AMIDE IN WHICH THE AMIDE GROUPS FORM AN INTEGRAL PART OF THE MAIN POLYMER CHAIN WHICH INCLUDES THE STEPS OF DISSOLVING WASTE MATERIAL FORMED OF SAID SYNTHETIC PLASTIC IN FORMIC ACID, MIXING A HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF N-HEXANE, N-HEPTANE, CYCLOHEXANE, HEXENE, CYCLOHEXENE, BENZENE, AND TOLUENE WITH THE SOLUTION IN AN AMOUNT SUFFICIENT TO FORM AN AZEOTROPIC MIXTURE, THEN HEATING THE AZEOTROPIC MIXTURE TO A TEMPERATURE SUFFICIENTLY HIGH TO VAPORIZE THE AZEOTROPIC MIXTURE AND REMOVING THE VAPORS FROM THE DISTILLATION ZONE TO LEAVE BEHIND THE DESIRED SAID SYNTHETIC PLASTIC. 